1. Field of the Invention
The invention is directed to an actuation device for machine elements exhibiting wear-induced play, especially for brakes in rail vehicles, with a piston-cylinder unit which generates an actuation force and which has a piston rod which cooperates with a readjusting device which compensates for play caused by wear.
2. Description of the Related Art
In the present application, machine elements exhibiting wear-induced play are considered to be machine elements such as clutches or brakes. Machine elements of this type are used particularly for transmitting driving and braking forces in rail vehicles. To interrupt and close the flow of force, facings are used which withstand high thermal stresses on the one hand and enable a favorable progression of the force flow on the other hand. These facings are exposed to wear which causes a gradually increasing play. Readjusting devices are known for compensating this wear-induced play.
For example, a prior art actuation device is disclosed by European reference EP 0 174 690 having an adjusting nut/spindle assembly as a readjusting device for brakes. This prior art readjusting device is based on a control sleeve under a spring force. A first clutch operated by the spring force prevents an adjusting nut from rotating and causing a longitudinal adjustment of the piston spindle by a rotating movement. After traversing a predetermined play path, the first clutch is released by the displacement of the piston rod beyond a determined path, so that the adjustment of the play path can be increased corresponding to the wear that has occurred on the facing. Another forward feed movement of the piston results in the engagement of a second clutch, whereupon the adjustment of the adjusting nut on the spindle is stopped. This known complicated mechanism for engaging and disengaging the adjusting nut is costly to manufacture because of both a large number of parts and a long and intricate assembly procedure. The structural component parts, especially the clutch, which are highly stressed mechanically through friction have a strong tendency to wear.
Another prior art readjusting device is disclosed in German reference DE-OS 22 01 082, in which the above-mentioned type of readjusting mechanism is used for rail vehicle brakes in connection with a piston-cylinder unit for brake actuation.